1. Field of the Invention
The present invention relates to PWM power controllers, and more particularly to an integrated average current limit and control for a PWM power supply.
2. Description of the Related Art
The current in the switching devices of pulse-width modulation (PWM) control circuitry has the characteristic shape of a ramp or ramp-on-a-step due to one or more output inductors. The current is converted to a voltage by either a small resistor in series with the source in the primary or by a current transformer or other transducer mechanism. The voltage waveform has historically been either integrated external to or peak detected on the controller chip. The resulting voltage information is then used to provide either current mode feedback information or current limiting information or, in some cases, both. In some applications, it is desirable to provide either the current limiting or current feedback function based on the average value of the ramp-on-a-step waveform. Conventional methods estimate the average value based on the sampled peak value. Such conventional techniques, however, are inaccurate and cause current tail-out.